KR100355989B1 - Adaptive Code Division Multiple Access for Compensation of Signal Attenuation in Wireless Communication System - Google Patents

Abstract

The present invention relates to an adaptive code division multiple access (CDMA) method for signal attenuation compensation in a wireless communication system, and more particularly, to a terminal station in a wireless communication system using a CDMA scheme. Rainfall attenuation is reported to the control station, and the control station estimates the degree of attenuation that the terminal station will experience at the next time point according to the attenuation amount reported from the terminal station to determine the number of orthogonal codes to be allocated to each terminal station among the stored orthogonal codes. And assigns an orthogonal code determined by the control station to the corresponding terminal station, and the terminal station determines and transmits an orthogonal code to be transmitted for each piece of information data among the orthogonal codes assigned at the transmitting end, and receives information from the received orthogonal code at the receiving end. The present invention relates to an adaptive CDMA method for performing data extraction.

According to the present invention, when a fading of a signal occurs in a wireless communication system using a CDMA scheme, the attenuation can be adaptively overcome according to the amount of attenuation experienced by the user. If there is a decrease in link availability, there is an advantage in that performance and link availability can be increased without increasing the additional complexity of the conventional hardware.

Description

Adaptive Code Division Multiple Access for Signal Attenuation Compensation in Wireless Communication System

The present invention relates to an adaptive code division multiple access (CDMA) method for signal attenuation compensation in a wireless communication system, and more particularly, to a terminal station in a wireless communication system using a CDMA scheme. Rainfall attenuation is reported to the control station, and the control station estimates the degree of attenuation that the terminal station will experience at the next time point according to the attenuation amount reported from the terminal station to determine the number of orthogonal codes to be allocated to each terminal station among the stored orthogonal codes. And assigns an orthogonal code determined by the control station to the corresponding terminal station, and the terminal station determines and transmits an orthogonal code to be transmitted for each piece of information data among the orthogonal codes assigned at the transmitting end, and receives information from the received orthogonal code at the receiving end. The present invention relates to an adaptive CDMA method for performing data extraction.

In information society such as modernization, communication technology is one of the core technologies and the biggest issue in such communication is 'how can we achieve the maximum transmission speed in limited environment?'

This is a concern about a communication technology that achieves the maximum effect at the minimum cost, and the solution to this problem is a multiple access method.

The multiple access method refers to a technology that maximizes the circuit utilization rate by efficiently using limited resources. As a result of research by various engineers for a long time, various various methods exist. The most representative methods are the time division multiple access (TDMA) method and the frequency division multiple access method. And Code Division Multiple Access.

In the time division multiple access scheme, each radio channel is composed of several time slots, and each user is assigned a specific frequency / time interval. Therefore, only one mobile station in a cell can use a given frequency at a specific time.

The code division multiple access scheme distributes one cell in one wide band, and each signal is spread with different codes to distinguish them. TDMA and CDMA have the advantage that the base station's wireless hardware can be used by multiple users, and the digital system can accommodate more subscribers per base station and frequency band, providing economical service even in dense areas.

The conventional TDMA and CDMA will be described in more detail.

TDMA, as its name implies, is a method of transmitting information by dividing time.

It is not always necessary to use all lines in the voice network, and since the amount of information occupied by the voice is not large enough to occupy the entire line, it is possible to increase the efficiency of the line by collecting the small amount of information and transmitting them on one line. For example, when several people talk to each other in sequence when they talk, the transmission band is divided into time slots in the time base by applying the principle that everyone can talk by sharing time one by one. A method of allowing a terminal device to be connected to a plurality of base stations in one transmission band (frequency channel) by assigning each time slot to a plurality of terminal devices (mobile stations).

The TDMA system includes a GSM (Group Special Mobile) in Europe, an IS-54 in North America, and a Personal Digital Cellular (PDC) in Japan.

The Conference of European Postal and Telecommunication Administrations (CEPT) organized the Group Special Mobile in 2004 to complain about user's dissatisfaction due to the existence of several analog mobile communication systems in Europe and to connect the digital wired network. GSM system. Initially aimed at better quality and data transfer across Europe, Roaming, FAX, E-mail, File, etc., resulting in side effects such as low cost system and increased frequency efficiency. Considering the openness of the system.

GSM consists of 8 time intervals per radio channel, and each user transmits every 8th time interval and receives during that time interval. Therefore, the base station needs to install only one fast transceiver per 8 channel, and it is easy to design the duplex filter of the mobile station by transmitting / receiving slot staggering, and it transmits during the period between the transmission time period and the reception time period. It is available. In addition, Interference Diversity is implemented by using frequency hopping that changes frequency at each time interval, and is particularly useful for discontinuous transmission.

CDMA is a completely different method. The basic development of CDMA was made in the 1960s for military purposes, and at that time there was a greater emphasis on encryption than on multiplexing. The method developed at this time was CDMA of FS (Frequency Hoping) method, and the principle of this method was to use random number table to select which frequency when transmitting any information without ever knowing which frequency to use.

This method is still used in military radios. In this case, the multiplexing efficiency is low, but the encryption may have high reliability.

The CDMA scheme developed for cellular systems has been standardized by IS-95 in the United States, with the limitations of QUALCOMM.

Due to the explosive demand of analog mobile subscribers, it is required to introduce digital mobile communication system in the premises.In 1991, the company established a joint development contract with QUALCOMM, a CDMA proposal company, and started to develop basic call processing functions. It was completed in April 1994 and has been successfully operated in mobile communication to date.

In order to explain CDMA, we briefly describe IS-95, the American Common Air Interface (CAI) standard.

In North America's CDMA CAI, IS-95, many users share a common channel for transmission, and the basic channel rate is 9.6kb / s. This is a combination of technologies, spreading at a channel chip rate of 1.2288 Mchips / s with a spread rate of 128, which is different from the forward link (transmission from base station to mobile station) and the reverse radio link. In the case of the omni link, the user's data flow is encoded with a half-rate convolutional coding, interleaved, and spread by one of 64 Walsh Function Sequences. Each mobile station in a given cell is given a different spreading sequence so that in the case of at least one passage channel it can be completely isolated from the signals of different users. In order to reduce the disturbance between mobile stations using the same spreading sequence of different cells and to obtain the required wideband spectral characteristics, all signals in each cell are scrambled using a pseudo random sequence of 215 length chips. )do. Orthogonality is maintained because their signals are scrambled equally among users in a cell.

A pilot channel is provided for the prediction of the channel on the forward link, and has a larger transmit power than the user traffic channel. In the case of reverse transmission, since a signal received at each base station is received through a different transmission channel, a different spreading scheme should be used.

The user data is first 1/3 convolutionally coded, interleaved, and then mapped to six coded symbols corresponding to one of 64 Orthogonal Walsh Functions. The final spread 307.2 kchip / s chip flow rate is then diffused into a user-specified chip with four times the spread of 1.2288 Mchips / s. It is designed to be strong against disturbance by mapping corresponding to 1/3 rate encoding and Walsh code.

In the reverse radio link, the near-far problem is solved by controlling the mobile station transmit power. Power control uses open-loop control and fast closed-loop control. Closed-loop control is performed at a speed of 800 b / s, and control signals are transmitted in a voice frame. Rake receivers are used to combine multipath components with base stations and mobile stations and to reduce attenuation amplitudes.

Increased capacity, no need of frequency planning to allocate to the cell, the ability to transmit data at various data rates can be overcome, including variable speech coding, power control, fading margin, and forward error correction. Correction, etc. are introduced to reduce the required RF transmission power.

One of the biggest challenges this multiplexing method has to overcome is the damping effect. Attenuation is caused by free space loss caused by the propagation of radio waves from a transmitting antenna into three-dimensional space, atmospheric attenuation due to the absorption of oxygen and water molecules in the atmosphere, and absorption and scattering of rainfall particles during rainfall. Rainfall attenuation, bush attenuation caused by absorption and scattering by tree trunks and leaves on propagation paths, reflection and diffraction.

In order to overcome such attenuation, an adaptive multiple access method is used in which a TDMA scheme can overcome the attenuation by determining an attenuation degree of a terminal station and transmitting an extra time slot to a user who is experiencing severe attenuation.

SUMMARY OF THE INVENTION The present invention has been made in view of this background and according to the amount of attenuation experienced by a terminal station in a wireless communication system using a CDMA method, the terminal station predicts the degree of attenuation experienced by the next time point and assigns it to the corresponding one of the stored orthogonal codes. The number of orthogonal codes is determined, the determined orthogonal codes are assigned to the corresponding terminal station, and the terminal station determines and transmits the orthogonal codes to be transmitted for each information data among the orthogonal codes assigned at the transmitting end, and the receiving end is received. An object of the present invention is to provide an adaptive fading overcoming method for performing an operation of extracting information data from an orthogonal code.

1 is a block diagram illustrating an operation principle of an adaptive multiple division access in a CDMA wireless communication system according to an exemplary embodiment of the present invention.

2 shows the bit error probability according to the change of Mr when using the BPSK modulation scheme in the adaptive CDMA system according to a preferred embodiment of the present invention.

3 is a flowchart illustrating an adaptive CDMA method for signal attenuation compensation in a wireless communication system according to a preferred embodiment of the present invention.

As shown in FIG. 4, when the adaptive CDMA is used, the outage probability is improved compared to the case where the adaptive CDMA is not used.

<Description of Signs of Major Parts of Drawings>

100: control station 200: terminal station

210: transmitting end of the terminal station 220: receiving end of the terminal station

In order to achieve the above object, the present invention reports a signal attenuation amount from a terminal station to a control station in a CDMA wireless communication system environment including a transmission and reception terminal station (User) and a control station (Base Station). The number of orthogonal codes is determined by predicting the degree of attenuation that the terminal station will undergo at the next time according to the reported attenuation, and assigning the orthogonal codes to the terminal station among the orthogonal sequences stored by the control station. The terminal station determines and transmits an orthogonal code to be transmitted for each information data among the orthogonal codes assigned by the transmitting end, and the receiving end performs the task of extracting the information data from the received orthogonal code. It is done.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention may be easily implemented by those skilled in the art in detail.

1 is a block diagram illustrating an operation principle of an adaptive multiple division access in a CDMA wireless communication system according to an exemplary embodiment of the present invention.

As shown, first, the user station 200 puts attenuation information experienced by the terminal station 200 at a predetermined time interval in a control signal transmitted to the control station 100 to control station 100 (Base Station). Report).

At this time, the degree of attenuation of the terminal station 200 transmitted to the control station 100 is determined by measuring the signal energy to interference ratio (SIR) of the received signal or measuring the strength of the satellite signal or pilot signal. Can be.

The control station 100 determines the signal attenuation degree of the terminal station link according to the reported attenuation information, determines the number Mr of orthogonal codes (spread codes: Orthogonal Sequence) for data spreading of the terminal station 200, and then determines Orthogonal Sequences according to Mr are allocated to the terminal station 200.

Here, Mr is an orthogonal code number assigned to a single terminal station 200 and depends on the amount of attenuation of the terminal station 200. However, if the attenuation of the terminal station 200 is severe, the Mr value is also the total assignable orthogonality of the control station 100. It is limited by the number of extra orthogonal codes Mf (= Mt-Mu) that is a difference from the number of codes Mt, which is the number of orthogonal codes used in all terminal stations. Therefore, the duplication of orthogonal codes is impossible and Mr must be smaller than Mf.

In a typical CDMA system, a transmitting end 210 of a terminal station encodes and interleaves transmission data, and then transmits the data by one of orthogonal codes assigned to reduce interference between users. ) Orthogonal codes corresponding to the information bit streams to be transmitted through the transmitting terminal 210 of the terminal station among the allocated orthogonal codes are selected and used. The transmission of information bits is possible.

As an example of the modulation process, as described above, the terminal station 200 selects one orthogonal code from the orthogonal codes allocated from the control station 100 and transmits a data bit. It can be said to select one of the Mr orthogonal codes allocated according to the bits.

In other words, if there are Mr orthogonal Since the number of bits of data can be determined by observing Mr data, the number of data bits k Mr.

In the case of the QPSK system, k + 2 bits may be QPSK modulated and transmitted simultaneously. That is, k data bits are observed to determine an orthogonal code to be transmitted, and 2 bits, that is, information of one symbol are transmitted. Since two bits are transmitted in one symbol in the QPSK system, transmitting the selected code using the multi-code method described above is the same as transmitting k + 2 bits. Thus, the same information rate is maintained and k / 2 + 1 times are used. Symbol repetition is possible.

In the BPSK system, k + 1 symbol repetition is possible because k bits are observed and a transmission code is used and one bit of information is sent.

If the same data rate is maintained, symbol repetition is possible, and thus reduction of symbol energy due to signal attenuation can be overcome. In this case, the larger the Mr, the more information can be transmitted and thus more symbol repetition is possible.

2 shows the bit error probability according to the change of Mr when using the BPSK modulation scheme in the adaptive CDMA system according to a preferred embodiment of the present invention.

As mentioned above, the number of symbol repetitions that can be used in each modulation scheme is k + 1 for BPSK. As shown in FIG. 2, it can be seen that the performance improves as the Mr value increases, since the number of times the symbol can be repeated increases as the Mr value increases.

As can be seen from the above, it can be seen that the adaptive CDMA system proposed in the present invention shows better performance as Mr becomes larger. In the bit error rate curve shown in FIG. 2, the dotted lines indicate bits of the general synchronous CDMA system. Error probability, and the solid lines are the bit error probability of adaptive CDMA according to Mr.

When the reference BER is set to 10 ^ -6, the performance improvement of 2.3dB, 3.1dB, 3.7dB, 4.2dB, and 4.5dB is achieved when Mr = 8, 16, 32, 64, and 128, respectively, compared to the general synchronous CDMA system. Can be.

For example, the adaptive allocation method of Mr according to the degree of attenuation of the terminal station 200 will be described.

If the power margin (variable for the system to maintain the quality of the transmission signal) is Fm, and the reported rainfall attenuation is alpha, the orthogonal code number Mr of the terminal station 200 may be adaptively determined as follows.

If (alpha = Fm) then Mr = 1;

If (Fm alpha <= Fm + G8) then Mr = 8;

If (Fm + G8 alpha <= Fm + G16) then Mr = 16;

If (Fm + 16 alpha <= Fm + G32) then Mr = 32;

If (Fm + G32 = alpha) then Mr = 64;

In this case, Gx is a power gain obtained by referring to FIG. 2.

Based on the above description, an embodiment of the adaptive CDMA used for signal attenuation compensation in a practical environment will be described.

3 is a flowchart illustrating an adaptive CDMA method for signal attenuation compensation in a wireless communication system according to a preferred embodiment of the present invention.

The terminal station 200 reports the amount of attenuation measured in units of time to the control station 100 (step: S1). The control station 100 predicts the amount of attenuation that the terminal station 200 will experience at the next time point based on the amount of attenuation reported from the terminal station 200 (step: S2).

Subsequently, the control station 100 checks whether the predicted amount of attenuation changes with the amount of attenuation that can be overcome by using the attenuation region at the previous time, that is, the orthogonal code currently assigned (step S3). If there is no change, return to the initial state and continue the prediction work according to the received attenuation, and if there is a change, determine whether the currently estimated attenuation is within the compensable range (step: S4), and then select the appropriate attenuation area. The orthogonal code Mr is determined (step: S5), and accordingly, Mr orthogonal codes are assigned to the terminal station 200 (step: S6).

When the orthogonal code assignment to the terminal station 200 ends, the control station 100 records the attenuation area at the present time and returns to the initial state (step: S7).

On the other hand, the terminal station 200 measures the amount of attenuation currently experienced by the terminal station 200 on a predetermined time basis, and reports the measured amount of attenuation to the control station 100.

In the terminal station 200, after receiving the orthogonal codes determined previously from the control station 100, the number of data bits for determining the orthogonal codes to be transmitted through the mobile communication network among the notified orthogonal codes (code determination bit number: k) (Step: S8).

When the number of data bits k is determined, the determined k orthogonal codes are observed to determine the transmission orthogonal codes to be transmitted among the M orthogonal codes (step S9). Step: S10).

Subsequently, as described above, the code is repeatedly transmitted as many symbols as possible according to the modulation scheme (BPSK, QPSK, etc.) (step S11).

On the other hand, the receiving terminal 220 of the terminal station determines the transmitted orthogonal code by observing the received signal by the number of repetitions according to the modulation scheme, and determines the k data bits corresponding to the orthogonal code.

Figure 4 shows the outage probability before and after applying the adaptive CDMA (rainfall environment in the BPSK modulation satellite communication system) according to a preferred embodiment of the present invention.

The outage probability is defined as the percentage of time that attenuation is greater than the established fade margin for the entire observed rainfall event time.

As shown in FIG. 4, when the adaptive CDMA is used, the outage probability is improved compared to the case where the adaptive CDMA is not used.

As mentioned above, although preferred embodiments of the present invention have been described in detail, those of ordinary skill in the art to which the present invention pertains should realize the present invention without departing from the spirit and scope of the present invention as defined in the appended claims. It will be appreciated that various modifications or changes can be made. Accordingly, modifications to future embodiments of the present invention will not depart from the technology of the present invention.

As described above, according to the present invention, according to the amount of attenuation experienced by the terminal station in the wireless communication system using the CDMA method, the terminal station estimates the degree of attenuation experienced by the next time point and allocates it to each terminal station among the stored orthogonal codes. The number of codes is determined and assigned to the corresponding terminal station, and the terminal station provides an adaptive fading overcoming method for determining the type of code assigned to each data value accordingly. If fading occurs, the attenuation can be adaptively overcome, depending on the amount of attenuation experienced by the user, thus significantly reducing service performance and link availability due to signal attenuation. There is an advantage that can increase performance and link availability without increasing complexity.

Claims (5)

In a code division multiple access (CDMA) wireless communication system including a user station and a control station (base station) including a transceiver, Measuring, by the terminal station, the amount of attenuation currently experienced by the link of the terminal station on a predetermined time basis and reporting the measured amount of attenuation to the control station; The control station determines the amount of attenuation that the terminal station will experience at the next time point based on the amount of attenuation reported from the terminal station, and determines the Orthogonal Sequences of Mr to be stored by the terminal station based on the identified amount of attenuation. step; Assigning, by the control station, the determined orthogonal code to the terminal station; Determining, by the transmitting end of the terminal station, an orthogonal code for spreading each transmission data bit among the allocated Mr orthogonal codes, and modulating and transmitting symbol information corresponding to the transmission data bit with the determined orthogonal code; Adaptive CDMA method for signal attenuation compensation in a wireless communication system comprising a. The method of claim 1, wherein the transmitting step, Determining, by the terminal station, the number of data bits k according to each orthogonal sequence allocated from the control station; The terminal station transmitting end observes the transmission data bits by the determined number of data bits, determines an orthogonal code corresponding to each transmission data bit of the Mr orthogonal codes, and maps the orthogonal codes to the transmission data bits, respectively. step; Transmitting, by the terminal station transmitting end, symbol information corresponding to the transmitted data bits through the mapped orthogonal code; Transmitting, by the terminal station transmitting terminal, symbol repetition as many times as possible according to a modulation scheme; And The receiving end of the terminal station observes the received signal by the number of repetitions according to the modulation scheme to determine the orthogonal code transmitted from the received signal, and determining k data bits corresponding to the determined orthogonal code. Adaptive CDMA method for signal attenuation compensation in a wireless communication system, characterized in that. 3. The adaptation for signal attenuation compensation in a wireless communication system according to claim 2, wherein in determining the number of data bits k, the number of data bits is determined to be equal to the binary log value of the Mr. Type CDMA method. 3. The adaptive CDMA method for signal attenuation compensation in a wireless communication system according to claim 2, wherein the modulation scheme is a phase modulation scheme (PSK). 2. The adaptive CDMA method for signal attenuation compensation in a wireless communication system according to claim 1, wherein in the Mr determining step, the Mr increases as the amount of attenuation of the terminal station increases.